1. Field of the Invention
The present invention relates to a communication technique, and in particular, to a terminal apparatus for transmitting or receiving a signal including predetermined information.
2. Description of the Related Art
Consideration of road-to-vehicle communications is underway to prevent encounter head traffic accidents at intersections. In the road-to-vehicle communication, information on the situations of an intersection are communicated between a road-side apparatus and on-vehicle equipment. In the road-to-vehicle communication, it becomes necessary to install the road-side apparatuses, which requires large efforts and high cost. On the other hand, in inter-vehicle communication, i.e., in a mode in which information is communicated between on-vehicle equipment, it becomes unnecessary to install the road-side apparatuses. In this case, it is determined, by detecting at real-time current location information with, for example, a GPS (Global Positioning System), etc., and by exchanging the location information between the on-vehicle equipment, which road each of a driver's vehicle and other vehicles exists on, the road entering an intersection.
In a wireless LAN (Local Area Network) in accordance with the specification of IEEE 802.11, etc., an access control function called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is used. Accordingly, in the wireless LAN, the same wireless channel is shared by a plurality of terminal apparatuses. In such CSMA/CA, a packet signal is transmitted after it has been confirmed that another packet signal is not transmitted by carrier sense.
When a wireless LAN is applied to inter-vehicle communication, such as ITS (Intelligent Transport Systems), it is desirable that a signal is transmitted by broadcast transmission because it is needed to transmit the information to an unspecified majority of terminal apparatuses. Further, if road-to-vehicle communication is performed in addition to inter-vehicle communication, the communication becomes more complicated.
The information, which are necessary for safe driving, such as construction information and regulation information, and which do not affect the existing location of each vehicle, are generally stored in a server, etc. Road-to-vehicle communication is suitable for the delivery of the information stored in a server, etc. However, in a transitional situation or in a district in which the number of the installed road-side apparatuses is small, the area of road-to-vehicle communication becomes narrow. Accordingly, the information necessary for safe driving, such as construction information and regulation information, cannot be sufficiently delivered. On the other hand, delivery of these information should be limited to an area or period of time that may be affected by these information, from the viewpoint of effectively using frequencies.